The claimed invention relates to a method for compounding a plastic material, to a plastic material, and to a plastic product which is made from this plastic material.
From DE 10 2006 033 897 A1 a thermoplastic elastomer is known which consists of a propylene copolymer of propylene and at least a further alkene, an ethylene copolymer of ethylene and at least a further alkene, an ethylene-propylene-diene rubber and a filler material for the modification of surface-forming properties of the thermoplastic elastomer. Thereby, all ingredients are mixed with a cross-linking agent and are conjointly cross-linked with each other for producing this thermoplastic elastomer.
Also from WO 2006/070179 A1 a thermoplastic elastomer is known which is made from a propylenic olefin polymer, an ethylenic polymer, a cross-linking agent, a generator of free radicals and optionally a high density polyethylene. Thereby, once again all ingredients are mixed with each other and are cross-linked with each other.
The physical properties of plastics strongly depend on the temperature. Thus, these properties at low temperatures, i.e. at temperatures below -30 C° , in particular below -32.5 C° , below -35 C.° and very particularly at temperatures of -37.5 C.° or below, cannot be compared with those at room temperature or even higher temperatures. Additionally, no stringent conclusions can be drawn from the physical properties which are measured by default at high temperatures as, e.g., 140 C.° or 230 C.° to the properties of the plastics at low temneratures.
The properties of a plastic at low temperatures have, e.g., a pivotal influence onto the usability of the plastic if it shall be used as material for a covering or a housing of an airbag for a motor vehicle. Thereby, it has to be guaranteed that a plastic used in such a way shows a reproducible rupture behavior also at low temperatures and that the formation of loose plastic particles is avoided at the same time.
The behavior of the plastic which is shown when it ruptures along a predetermined breaking point, e.g., by the deployment of an airbag (airbag activation) due to an accident shall here—in case of using a plastic for the production of a covering of an airbag—be understood as rupture behavior. Such rupture behavior can also be transferred onto other plastic products and other events initiating the rupture.
It was shown that airbag coverings or airbag housings which are made from various conventional materials like, e.g., thermoplastic elastomers based on olefins (TPO) or based on olefins, cross-linked rubber and styrol-ethene-butene-styrol (TPO/SEBS/TPV) still show a desirable rupture behavior at −32.5 C° , however, no longer at −35 C.° or −37.5 C° . An undesirable rupture behavior can, e.g., be manifested in that airbag coverings or housings do not any longer rupture along a predetermined breaking point, but rip uncontrolled and further parts of the material detach from the airbag covering during rupture or ripping (e.g., due to an airbag activation).
But also in case of materials known from prior art which guarantee a desirable rupture at low temperature, the problem occurs that their production can often not be effected in a reproducible way and is laborious.